1. Field of the Invention
This invention generally relates to a cylindrical torsion-detecting sleeve member. More specifically, the present invention relates to a torque-detecting device that uses the sleeve member.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. Recently, bicycles have been provided with cycle computers to inform the rider of various traveling conditions of the bicycle.
Bicycles are sometimes equipped with a torque sensor (e.g., a torque-detecting device) for detecting torque acting on an axle. One example of a torque sensor that is being developed uses magnetostrictive effects wherein magnetic force varies according to strain (see Japanese Laid-Open Patent Application Nos. 3-269330 and 2001-289720, for example).
The torque sensor disclosed in Japanese Laid-Open Patent Application No. 3-269330 has two solid shafts disposed concentrically, a thin cylindrical shaft connected in series between the two solid shafts, and a detection coil disposed on the external periphery of the thin cylindrical shaft. The thin cylindrical shaft has an effective surface area that is sufficiently smaller than that of the two solid shafts, and the solid shafts are magnetized in one direction along an axial core line. Magnetostrictive elements are affixed to the external peripheral surface of the thin cylindrical shaft. Two magnetostrictive elements are used, and these elements have uniaxial magnetic anisotropy so that their easy magnetization axes intersect. Disposing the magnetostrictive elements on the thin cylindrical shafts in this manner makes it possible to increase the amount of strain created in the magnetostrictive elements and to increase the sensitivity of detection even in cases in which the rotational torque is small.
In Japanese Laid-Open Patent Application No. 3-269330, the torque sensor is disclosed as detecting torque by using a thin cylindrical shaft. Therefore, the torsion is excessive when a comparatively large amount of torque is detected in the bicycle or the like. Also the sensitivity of detection may be reduced, leading to large measurement errors.
In Japanese Laid-Open Patent Application No. 2001-289720, the torque sensor is disclosed as having a sleeve with a magnetostrictive pattern formed in the external peripheral surface by inclining magnetostrictive members towards the core, a torque transmission shaft that fits into the internal peripheral surface of the sleeve, and a detection coil disposed on the external periphery of the sleeve. Concavities and convexities are formed in the external peripheral surface of the torque transmission shaft, and a hollow part is formed in the internal periphery. The sleeve is plastically bonded to the torque transmission shaft by expanding the diameter of the hollow part.
In the configuration of Japanese Laid-Open Patent Application No. 2001-289720, when a comparatively large amount of torque is detected and the stress acting on the torque transmission shaft exceeds a specified level, the residual stress in the interior of the torque transmission shaft may result in hysteresis, errors in sensor output, and measurement errors.
Thus, in the configurations of the conventional examples, measurement errors may occur when a large amount of torque is applied. Moreover, the range of torque detection is limited by the thickness or rigidity of the thin cylindrical member or the sleeve even when the amount of torque is small, and it is difficult to vary the range of torque detection.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved torsion-detecting sleeve member. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.